Film evaporator burner arrangement

ABSTRACT

A film evaporator burner arrangement ( 1 ) is provided, having: a combustion chamber arrangement comprising a combustion chamber ( 2 ) for the conversion of a fuel-air mixture with the release of heat, which extends in the axial direction along a longitudinal axis (Z); a combustion air supply ( 5 ) for the supply of combustion air, which is configured such that the combustion air is supplied with a tangential flow component to at least one combustion air inlet ( 8 ) of the combustion chamber arrangement; a film evaporator surface ( 4 ) for evaporating liquid fuel originating from a fuel film ( 10 ), which is arranged at a rear wall ( 3 ) axially rearward of the combustion air inlet ( 8 ); and a fuel supply ( 9 ) for the supply of liquid fuel to the film evaporator surface ( 4 ).

The present invention relates to a film evaporator burner arrangementand to a mobile heating appliance with such a film evaporator burnerarrangement.

In mobile heating appliances which are operated with liquid fuel, as areused in particular in parking heating systems or auxiliary heatingsystems in vehicles, conventional burner arrangements are used, in whichthe fuel is reacted with supplied combustion air in a combustion chamberwith release of heat. The reaction conventionally takes place withflaming combustion, wherein in principle however a partially or fullycatalytic reaction is also possible.

In the present context, a “mobile heating appliance” is understood tomean a heating appliance which is designed for use in mobileapplications and is adapted accordingly. This means in particular thatit is transportable (optionally fixedly installed in a vehicle or merelyaccommodated therein for transport) and is not designed exclusively forpermanent, stationary use, as is the case for example in the case ofheating a building. The mobile heating appliance may in this respectalso be installed fixedly in a vehicle (ground vehicle, ship etc.), inparticular in a ground vehicle. It may in particular be designed to heata vehicle interior, such as for example of a ground vehicle or water- oraircraft, and a partially open space, such as may be found for exampleon ships, in particular yachts. The mobile heating appliance may also beput to temporary stationary use, such as for example in large tents,containers (for example portable buildings for construction sites), etc.In particular, the mobile heating appliance may be designed as a parkingheating system or auxiliary heating system for a ground vehicle, such asfor example for a caravan, a motorhome, a bus, a car etc.

In the case of burner arrangements conventionally used in such mobileheating appliances, it is possible to distinguish between “atomizingburners”, in which the liquid fuel is injected with an atomizing nozzleand mixed with combustion air, and “evaporator burners”, in which theliquid fuel is evaporated starting from an evaporator region of theburner arrangement. In evaporator burners, as typically used in mobileheating appliances, the liquid fuel is conventionally supplied in liquidform to a porous, absorbent evaporator element, in which the fuel isdistributed by capillary forces and starting from which the liquid fuelis evaporated with absorption of heat of evaporation. The evaporatedfuel is in this case mixed with supplied combustion air to yield afuel-air mixture and the fuel-air mixture is reacted in the combustionchamber with release of heat. With such conventional evaporator burners,the problem arises that the material of the porous, absorbent evaporatorelement is attacked over time by the thermal load and the mediasurrounding it and possibly destroyed. The problem further consists inthe fact that over time deposits form in the evaporator element, whichcomplicate distribution and evaporation of the liquid fuel.

It is an object of the present invention to provide an improved burnerarrangement and an improved mobile heating appliance with such a burnerarrangement.

The object is achieved by a film evaporator burner arrangement asclaimed in claim 1. Advantageous further developments are indicated inthe dependent claims.

The film evaporator burner arrangement comprises: a combustion chamberarrangement, which comprises a combustion chamber for reacting afuel-air mixture with release of heat, which combustion chamber extendsin an axial direction along a longitudinal axis; a combustion air feedfor supplying combustion air, which is configured in such a way thatcombustion air with a tangential flow component is supplied to thecombustion chamber arrangement at at least one combustion air inlet; afilm evaporator surface for evaporating liquid fuel starting from a fuelfilm, which is arranged on a rear wall axially to the rear of thecombustion air inlet; and a fuel feed for supplying liquid fuel to thefilm evaporator surface.

Since the film evaporator burner arrangement takes the form of anevaporator burner, relatively small heating powers may also be reliablyprovided, as is often desired in mobile heating appliances. Through itsconfiguration as a film evaporator burner arrangement with a filmevaporator surface for evaporating liquid fuel, the problems whichconventionally arise in evaporator burners which comprise porous,absorbent elements, such as in particular deposit formation in theevaporator element, high electricity consumption when starting theburner arrangement for heating up the evaporator element, elevated wastegas emissions on starting and termination of combustion operation due tofuel residues in the evaporator element, etc., are avoided, sinceevaporation of the liquid fuel in the film evaporator burner arrangementtakes place starting from a film of the liquid fuel distributed on thefilm evaporator surface. The arrangement of the film evaporator surfaceaxially to the rear of the at least one combustion air inlet in thiscase enables defined input of heat from the combustion process in thecombustion chamber to the film evaporator surface by way of heatradiation and targeted convection. At least one combustion air inlethere means that a plurality of separate combustion air inlets may forexample also be provided, wherein even in the case of such a pluralityof combustion air inlets, the film evaporator surface is nonethelessarranged to the rear of the respective combustion air inlets relative tothe axial direction. The film evaporator surface may in this case beformed, for example, by a substantially smooth metallic area of the rearwall. However, it is for example also possible to provide the filmevaporator surface purposefully with roughening or fine texturing, so asto improve wetting and fuel distribution as well as evaporationbehavior. The rear wall may here in particular be formed by a rear wallof the combustion chamber arrangement, i.e. of the combustion chamberitself or a pre-evaporation chamber arranged flow-wise upstream thereof,or for example also by a rear wall of an evaporation region arranged inthe combustion chamber arrangement. By supplying the combustion air witha tangential flow component, i.e. with swirl, good distribution of theliquid fuel at the film evaporator surface is achieved and stabilizationof the flame in the combustion chamber is furthermore achieved. Thesupplied combustion air thus comprises a direction component in thecircumferential direction, but may preferably also comprise furtherdirection components, for example directed radially inwards and/or inthe axial direction. The combustion air is preferably supplied to thecombustion chamber arrangement with very strong swirl. The filmevaporator burner arrangement according to the invention then enablesoperation in which substantially no deposits are formed from the fuel.The combustion chamber may in particular be configured for reaction ofthe fuel-air mixture under flaming combustion; however, a configurationfor reaction of the fuel-air mixture under partially or fully catalyticcombustion is for example also possible. The fuel feed is in this casepreferably configured such that the liquid fuel is supplied withoutatomization or nebulization to the film evaporator surface, particularlypreferably flowing out thereto at low pressure. The fuel feed in thiscase does not comprise any atomization nozzles.

If the combustion air is supplied to the combustion air inlet fromradially outside, particularly good distribution of the fuel film on thefilm evaporator surface is achieved. The combustion air thus has both atangential and a radially inwardly directed flow component.

If the film evaporator surface is configured to be free of porous,absorbent bodies, deposit formation on the film evaporator surface maybe reliably prevented. Low-deposit evaporation is achieved in particularwith a combination of low component temperatures and a configurationfree of porous, absorbent bodies.

According to one further development, the film evaporator surfaceextends predominantly perpendicularly to the longitudinal axis. In thiscase, the film evaporator surface may for example extend in asubstantially planar manner, or indeed have a convexly outwardly curvedshape or a concavely inwardly curved shape or the like. The filmevaporator surface may preferably extend over substantially the entirecross-section of the rear wall of the combustion chamber arrangement toachieve as large as possible an area of fuel evaporation.

According to one refinement, the combustion air supply is configuredsuch that the combustion air with the tangential flow component issupplied to the combustion chamber. In this case, the combustion chamberarrangement does not have a pre-evaporation chamber for pre-processing afuel-air mixture prior to inlet into the combustion chamber, but rathermixing of the evaporated fuel with the supplied combustion air to yielda fuel-air mixture takes place in the combustion chamber itself. In thiscase, a structurally particularly simple and inexpensive embodiment isthus made possible.

According to one further development, the combustion chamber arrangementcomprises a pre-evaporation chamber arranged flow-wise upstream of thecombustion chamber for pre-processing a fuel-air mixture prior to entrythereof into the combustion chamber. A pre-evaporation chamber is hereunderstood to mean a region of the combustion chamber arrangement inwhich evaporation of fuel and intermixing of evaporated fuel withsupplied combustion air to yield a fuel-air mixture takes place, but inregular operation of the burner no exothermic reaction of the mixturetakes place, in particular no flame forms. The pre-evaporation chambertherefore does not itself form part of the combustion chamber, butrather is arranged flow-wise upstream thereof. The pre-processing of thefuel-air mixture enabled in this way prior to entry thereof into thecombustion chamber allows particularly low-pollutant combustion.

According to one further development, the pre-evaporation chamber isseparated from the combustion chamber by a partition wall extendingradially inwards from a side wall of the combustion chamber arrangement.In this case, subdivision of the combustion chamber arrangement into thecombustion chamber and the pre-evaporation chamber arranged flow-wiseupstream thereof is achieved in a structurally particularly simple andthus inexpensive manner. Furthermore, the film evaporator surfacelocated at the rear wall of the combustion chamber arrangement mayparticularly advantageously be thermally insulated relative to thecombustion chamber as regards thermal conduction, such that input ofheat to the film evaporator surface may proceed mainly via heatradiation and convection. In this case, the input of heat to the filmevaporator surface may be very purposefully adjusted by the structuralconfiguration of the partition wall.

According to one further development, the partition wall extendsradially inwards and axially rearwards from the side wall. In this case,particularly advantageous flow control is achieved, in which the fuelfilm is distributed particularly reliably over the film evaporatorsurface.

According to one further development, the pre-evaporation chamber has asmaller cross-section than the combustion chamber in the directionperpendicular to the longitudinal axis and the flow cross-section widensabruptly on transition from the pre-evaporation chamber to thecombustion chamber. Abrupt widening is here understood to mean wideningwith a double opening angle of greater than 90°. In this case,particularly good flow stabilization is achieved.

According to one further development, the combustion air feed isconfigured such that the combustion air with the tangential flowcomponent is supplied to the pre-evaporation chamber. In this case,particularly efficient mixing of evaporated fuel and supplied combustionair to yield a fuel-air mixture may take place in the pre-evaporationchamber.

According to one further development, the fuel feed is configured suchthat the fuel with a tangential direction component is supplied radiallyfrom outside to the film evaporator surface. Preferably, the fuel is inthis case supplied to the combustion chamber arrangement substantiallyin the same direction as the combustion air. This type of fuel feedresults in particularly good distribution of the fuel film on the filmevaporator surface.

According to one further development, the combustion chamber isconfigured to be free of constrictions or contractions over its axialextent. In other words, the combustion chamber in this case has amaximally free flow cross-section. Since no constrictions orcontractions are present, a particularly robust embodiment with a longservice life is achieved. Due to the described geometric configurationof the combustion chamber, good stabilization of the flame isnonetheless achieved in the combustion chamber.

The object is also achieved by a mobile heating appliance with such afilm evaporator burner arrangement as claimed in claim 13.

Further advantages and further developments are revealed by thefollowing description of exemplary embodiments made with reference tothe appended drawings.

FIG. 1 is a schematic representation of a film evaporator burnerarrangement according to a first embodiment.

FIG. 2 is a schematic representation of a swirl body for the combustionair feed according to the embodiment.

FIG. 3 is a schematic representation of a film evaporator burnerarrangement according to a second embodiment.

FIG. 4 is a schematic representation of a film evaporator burnerarrangement according to a third embodiment.

FIG. 5 is a schematic representation of a film evaporator burnerarrangement according to a fourth embodiment.

FIG. 6 is a schematic representation of a first modification of thefourth embodiment.

FIG. 7 is a schematic representation of a second modification of thefourth embodiment.

FIG. 8 is a schematic representation of a third modification of thefourth embodiment.

FIRST EMBODIMENT

A film evaporator burner arrangement 1 according to a first embodimentis described in greater detail below with reference to FIG. 1 and FIG.2. The film evaporator burner arrangement 1 is designed for a mobileheating appliance, in particular for a parking heating appliance orauxiliary heating appliance for a motor vehicle, which in particularcomprises a heat exchanger (not shown) for transferring heat from theoutflowing combustion waste gases to a medium to be heated. The mediumto be heated may, for example in the case of a hot-air heater, take theform of air to be heated for a vehicle interior or, in the case of aliquid heater, take the form of a liquid to be heated in a liquidcircuit of a vehicle, in particular cooling liquid. The heat exchangermay, in a manner known per se, be configured such that it surrounds thecombustion chamber and/or a flame tube adjacent thereto substantially inthe manner of a cup.

The mobile heating appliance further comprises, in a manner known perse, a fuel delivery device for delivering the liquid fuel, which may inparticular take the form of diesel, gasoline, ethanol, or the like. Thefuel delivery device may in particular take the form of a fuel meteringpump. In addition, the mobile heating appliance comprises a combustionair delivery device for delivering the combustion air, which may inparticular take the form of a blower, a control unit for controllingoperation of the mobile heating appliance and further componentsnecessary for operation, which are not described in any greater detail,in particular for example temperature sensors, etc.

The film evaporator burner arrangement 1 according to the firstembodiment comprises a combustion chamber 2, which, in the exampleshown, is approximately cylindrical in shape and extends along alongitudinal axis Z. The combustion chamber 2 is boundedcircumferentially by a peripheral side wall 21, which may for example beformed from a high-temperature resistant steel. A main direction of flowH in which combustion waste gases flow out from the combustion chamber 2to the heat exchanger (not shown) extends substantially parallel to thelongitudinal axis Z.

The combustion chamber arrangement 1 is closed at the rear by a rearwall 3, which is formed in the first embodiment by a rear wall of thecombustion chamber 2. The rear wall 3 is formed on the side facing thecombustion chamber 2 as a film evaporator surface 4 on which a film ofthe liquid fuel is distributed, starting from which evaporation of theliquid fuel takes place. Although the schematic representation of FIG. 1shows a completely flat configuration of the rear wall 3, it is alsopossible, for example, to make the rear wall 3 convex or concave in thedirection of the combustion chamber 2. In the embodiment shown, the filmevaporator surface 4 takes the form of a substantially smooth metallicarea; however, it is for example also possible to provide the filmevaporator surface 4 with roughening or fine texturing, in order toimprove distribution of the liquid fuel, wetting of the film evaporatorsurface 4 and fuel evaporation.

A combustion air feed 5 shown schematically in FIG. 1 is additionallyprovided, via which combustion air with a significant tangential flowcomponent, i.e. strong swirl, is introduced into the combustion chamber2. The combustion air feed 5 represented schematically in FIG.

1 by arrows is in this case arranged in such a way that the combustionair is supplied to the combustion chamber 2 radially externally at theperipheral side wall 21 at a distance from the rear wall 3 of thecombustion chamber arrangement 1 and thus at a distance from the filmevaporator surface 4. The combustion air is thus introduced into thecombustion chamber arrangement 1 with one flow component, i.e. strongswirl, extending in the circumferential direction and with one radiallyinwardly directed flow component, such that swirling flow around thelongitudinal axis Z forms in the combustion chamber 2. To bring aboutthis swirling flow, the combustion air feed 5 comprises a swirl body 6with a plurality of air ducts or air blades, in order to impart thedesired strong swirl to the combustion air.

FIG. 2 is a diagrammatic representation of a possible embodiment of theswirl body 6. The swirl body 6 depicted by way of example issubstantially annular in shape and a plurality of combustion air ducts 7are formed in the wall of the swirl body 6, via which combustion air maypass from the outside of the swirl body 6 to the inside of the swirlbody 6. The combustion air is supplied to the combustion air ducts 7 onthe outside of the swirl body 6 via a combustion air delivery device, asshown schematically by fat arrows, flows through the combustion airducts 7 and enters the combustion chamber 2 on the inside of the swirlbody 6 at combustion air inlets 8. Although the exemplary embodimentshown schematically depicts four such combustion air inlets 8, fewerthan four, but at least one combustion air inlet 8, or more than fourcombustion air inlets 8 may also be provided. As a result of the curvedshape of the combustion air ducts 7, which additionally taper inwards,the combustion air is provided with strong swirl and at the same timeaccelerated, as shown schematically in FIG. 2 by thin arrows.

The combustion air passing from the swirl body 6 into the combustionchamber 2 at the combustion air inlets 8 thus has a significanttangential direction component, i.e. strong swirl, and also at least oneradially inwardly directed direction component. A fuel feed 9 isprovided which opens into the side wall 21 to the rear of the combustionair inlets 8 with regard to the main direction of flow H. Via the fuelfeed 9 liquid fuel, which may in particular take the form of gasoline,diesel, ethanol or the like, is supplied to the film evaporator surface4 at the rear wall 3. Although FIG. 1 shows just one fuel line and onefuel outlet to the film evaporator surface 4 in the form of fuel feed 9,it is also possible, for example, to provide a plurality of fuel linesand/or a plurality of fuel outlets. In the exemplary embodiment, theliquid fuel is likewise fed radially inwards and with a tangentialdirection component, which is preferably in the same direction as theswirl of the supplied combustion air, something which may be achievedfor example by corresponding orientation of the fuel outlet (or the fueloutlets).

As a result of the swirling flow of the combustion air formed in thecombustion chamber 2, the fuel exiting the fuel feed 9 is distributedover the film evaporator surface 4 at the rear wall 3, such that a fuelfilm 10 forms there, starting from which the liquid fuel is evaporatedor volatilized. The fuel film 10 is depicted schematically in FIG. 1 bya dashed line. As a result of the arrangement of the film evaporatorsurface 4 to the rear of the combustion air inlet 8 at which thestrongly swirled combustion air is supplied, the fuel film 10 consistingof the liquid fuel spreads out due to small axial and large tangentialflow components and the temperature input into the liquid fuel of thefuel film 10 may be adjusted in a very targeted manner.

Moreover, an ignition element 11 for starting the reaction of thefuel-air mixture is arranged in the combustion chamber 2, this beingformed in the schematically depicted exemplary embodiment for example bya glow plug. Although, in the exemplary embodiment shown, the ignitionelement 11 projects from radially outside into the combustion chamber 2,other arrangements of the ignition element 11 are also possible, inparticular the ignition element 11 may for example also project axiallyfrom behind through the rear wall 3 into the combustion chamber 2. Whenthe film evaporator burner arrangement 1 is in operation, the fuel-airmixture is firstly ignited in the combustion chamber 2 by means of theignition element 11, to start the reaction. Once a stable flame hasformed in the combustion chamber 2, the ignition element 11 may then beswitched off, for example, or be used in a manner known per se forexample also as a flame detector for monitoring the flame. Although, inthe exemplary embodiment depicted, the combustion chamber 2 isconfigured for reaction of the fuel-air mixture under flamingcombustion, a refinement for reaction in a partially or fully catalyticreaction is for example in principle also possible.

The temperature established at the film evaporation surface 4 duringoperation of the film evaporator burner arrangement 1 is determined bythe thermal energy introduced into the combustion chamber 2 by theflame. This thermal energy is here transferred by convection, via heatradiation and via thermal conduction in the material of the side wall21. Through suitable geometric design and material selection, theoptimum temperature for reliable evaporation of the liquid fuel duringoperation of the film evaporator burner arrangement 1 may beestablished. Experience shows that at very low temperatures below theinitial boiling point of the fuel or at very high temperatures above thefinal boiling point, evaporation or volatilization is possiblesubstantially without the formation of deposits. In addition, thethorough intermixing of the fuel film 10 results in the “washing off” ofincipient deposits on the rear wall 3, so enabling operation of the filmevaporator burner arrangement 1 at least substantially without depositsfrom the fuel.

As is depicted schematically in FIG. 1, the combustion chamber 2 isformed with an at least substantially free flow cross-section free ofconstrictions or contractions, so meaning that the flows of the gases inthe combustion chamber 2 may be adjusted as desired.

A film evaporator burner arrangement 1 has thus been described which isstructurally simple and inexpensive to produce. Since no additionalporous evaporator element is provided, problems concomitant with such anevaporator element are reliably avoided. The robust configurationresults in relatively low sensitivity with regard to componenttolerances, which likewise has a positive effect on manufacturing costs.Reduced deposit formation and thus a long service life, low emissionsand low sensitivity to coarse fuel impurities are also achieved. Theuseful evaporation area is variable, such that a large range ofdifferent heating powers can be provided and a large number of differentliquid fuels may be used. Furthermore, the electrical power consumptionneeded for fuel feed is low and smoke and odor formation on start-up andburn-out of the film evaporator burner arrangement 1 is greatly reducedcompared with evaporator burners with porous evaporator elements.

Second Embodiment

A second embodiment is described below with reference to FIG. 3. Toavoid unnecessary repetition, in the description of the secondembodiment the same reference signs as for the above-described firstembodiment are used for the corresponding components of the filmevaporator burner arrangement 100 according to the second embodiment.Moreover, only the differences from the above-described first embodimentwill be described in greater detail below.

The film evaporator burner arrangement 100 according to the secondembodiment depicted schematically in FIG. 3 differs from theabove-described first embodiment in that, in addition to the combustionchamber 2, the combustion chamber arrangement also comprises apre-evaporation chamber 12 arranged flow-wise upstream thereof forpre-processing the fuel-air mixture prior to entry thereof into thecombustion chamber 2, as described in greater detail below. Furthermore,the rear wall 3 of the combustion chamber arrangement, on which the filmevaporator surface 4 is formed, is not flat in the second embodiment butrather on the side facing the combustion chamber 2 is concave in shape,indeed substantially conical in shape in the specific example shown. Inthe second embodiment, the rear wall 3 of the combustion chamberarrangement and the film evaporator surface 4 are however not arrangedin the combustion chamber 2, in which reaction of the fuel-air mixtureproceeds with release of heat, but rather in the pre-evaporation chamber12 arranged flow-wise upstream thereof, such that the rear wall 3 of thecombustion chamber arrangement forms the rear wall of thepre-evaporation chamber 12. Furthermore, in the second embodiment theignition element 11 is arranged in such a way that it projects axiallythrough the rear wall 3 of the combustion chamber arrangement as far asinto the combustion chamber 2. In an alternative, it is however alsopossible for example to arrange the ignition element 11 differently, inparticular such that it projects radially from outside into thecombustion chamber 2, as in the above-described first embodiment.

In the film evaporator burner arrangement 100 according to the secondembodiment, the pre-evaporation chamber is separated from the combustionchamber 2 by a partition wall 13 projecting inwards from the peripheralside wall 21. In the schematically depicted exemplary embodiment, thepartition wall 13 extends from the side wall 21 radially inwards andaxially backwards with regard to the main direction of flow H. However,the partition wall 13 does not extend over the entire cross-section ofthe combustion chamber arrangement, but rather a central opening 14 isprovided, via which the fuel-air mixture pre-processed in thepre-evaporation chamber 12 may pass from the pre-evaporation chamber 12into the combustion chamber 2. In the example shown, the central opening14 is arranged substantially coaxially with the longitudinal axis Z andhas a substantially circular cross-section, but other shapes are inprinciple also possible. The partition wall 13 may for example be formedof the same material as the side wall 21, in particular high-temperatureresistant steel.

Unlike in the first embodiment, in the film evaporator burnerarrangement 100 according to the second embodiment the combustion airinlets 8, at which the combustion air exits with a tangential flowcomponent and at least also a radial flow component from the swirl body6, are however not arranged in the region of the combustion chamber 2but rather in the region of the pre-evaporation chamber 12.Consequently, the combustion air with the tangential flow component issupplied from radially outside to the pre-evaporation chamber 12. In thesecond embodiment too, the film evaporator surface 4 is arranged to therear of the combustion air inlets 8. Although FIG. 3 also schematicallyshows a plurality of combustion air inlets 8, the film evaporator burnerarrangement 100 again comprises at least one combustion air inlet 8. Thefuel feed 9 supplies the liquid fuel to the rear of the combustion airinlets 8 from radially outside to the film evaporator surface 4. Atleast the mouth of the fuel feed 9 is here preferably arranged in such away that the liquid fuel is introduced with a tangential directioncomponent which corresponds to the direction of swirl of the suppliedcombustion air.

As a result of the strong swirling of the combustion air supplied to thepre-evaporation chamber 12 and the surface forces between the rear wall3 and the liquid fuel, the supplied liquid fuel is distributed at leastpartially radially at the film evaporator surface 4 to form a fuel film10, as shown schematically by dashed lines in FIG. 3.

During operation of the film evaporator burner arrangement 100, thepartition wall 13, which separates the pre-evaporation chamber 12 fromthe combustion chamber 2, heats up such that the fuel film 10 formed atthe film evaporator surface 4 is heated and evaporated or volatilizedmainly by way of heat radiation. The fuel-air mixture pre-processed inthe pre-evaporation chamber 12 passes via the central opening 14 intothe combustion chamber 2, in which it is reacted with release of heat,for example under flaming combustion. As a result of the strong swirl ofthe fuel-air mixture supplied via the opening 14 and the backflow thusestablished in the combustion chamber 2 in a central region about thelongitudinal axis Z, the flame stabilizes itself in the combustionchamber 2. Since the combustion chamber 2 is configured with asubstantially free flow cross-section, free of constrictions andcontractions, advantageous flow conditions may form in the combustionchamber 2.

As a result of rear wall 3 tapering concavely or conically backwardstogether with the partition wall 13 extending radially inwards andaxially backwards, the centrifugal forces acting on the fuel film 10 maybe adjusted simply by way of selection of the precise shape of the rearwall 3, such that it may be ensured that the liquid fuel is neitherdistributed too quickly radially inwards at the film evaporator surface4 nor does it remain too long in the radially outer region.

Preferably, heat exchange by way of thermal conduction between thecombustion chamber 2 and the pre-evaporation chamber 12 may beminimized, which may be achieved in a technically simple manner forexample by suitable selection of materials with low coefficients ofthermal conductivity, smaller contact areas and structural barriers.This makes it possible to keep the rear wall 3 at low temperaturesduring operation of the film evaporator burner arrangement 100 and toheat and volatilize or evaporate the fuel film 10 predominantly by heatradiation.

With the axial arrangement of the ignition element 11 shownschematically in FIG. 3, it is furthermore possible, in particular ifthe ignition element 11 takes the form of a ceramic glow plug, to heatup the fuel film 10 evenly at the start of operation of the filmevaporator burner arrangement 100.

In addition to the advantages already described in relation to the firstembodiment, the refinement according to the second embodiment enablesparticularly low-emission operation due to the pre-processing of thefuel-air mixture in the pre-evaporation chamber 12 prior to entry intothe combustion chamber 2.

Third Embodiment

A third embodiment is described below with reference to FIG. 4. To avoidunnecessary repetition, in the description of the third embodiment thesame reference signs as for the above-described first embodiment areused for the corresponding components of the film evaporator burnerarrangement 200 according to the third embodiment. Moreover, only thedifferences from the above-described first embodiment will be describedin greater detail below.

The film evaporator burner arrangement 200 according to the thirdembodiment depicted schematically in FIG. 4 differs from theabove-described first embodiment in that combustion air is not suppliedto the combustion chamber arrangement radially from outside at the sidewall 21, but rather the combustion air with the tangential flowcomponent is supplied to the combustion chamber arrangementsubstantially in the axial direction. The film evaporator surface 4 isarranged at a set-back rear wall 3 of the combustion chamberarrangement.

Although it has been described in relation to each of the embodimentsthat all the combustion air is supplied via the swirl body 6,modifications are also possible in which only part of the combustion airis supplied via the swirl body and the remaining combustion air issupplied to the combustion chamber arrangement for example at anotherpoint.

Fourth Embodiment

A fourth embodiment is described below with reference to FIG. 5. Toavoid unnecessary repetition, in the description of the fourthembodiment the same reference signs as for the above-describedembodiments are used for the corresponding components of the filmevaporator burner arrangement 300 according to the fourth embodiment.Moreover, only the differences are described in greater detail below.

In the fourth embodiment shown schematically in FIG. 5 too, thecombustion chamber arrangement comprises not only the combustion chamber2 but also a pre-evaporation chamber 12 arranged flow-wise upstreamthereof for pre-processing the fuel-air mixture prior to entry thereofinto the combustion chamber 2. In the fourth embodiment, the rear wall 3of the combustion chamber arrangement and the film evaporator surface 4are again arranged not in the combustion chamber 2 but in thepre-evaporation chamber 12 arranged flow-wise upstream thereof, suchthat the rear wall 3 of the combustion chamber arrangement forms therear wall of the pre-evaporation chamber 12. Also in the fourthembodiment, the ignition element 11 is arranged, similarly to in thesecond embodiment, in such a way that it projects axially from the backinto the pre-evaporation chamber 12.

In the fourth embodiment, the liquid fuel is supplied via the fuel feed9 from radially outside to the rear wall 3 comprising the filmevaporator surface 4. Also in the fourth embodiment, the fuel feed opensinto the combustion chamber arrangement axially to the rear of thecombustion air inlets 8. The combustion air inlets 8 are here arrangedin such a way that the combustion air is supplied with strong swirl fromradially outside into the pre-evaporation chamber 12.

As FIG. 5 shows, the pre-evaporation chamber 12 has a significantlysmaller cross-section in the direction perpendicular to the longitudinalaxis Z than the combustion chamber 2. In the case of a substantiallycylindrical refinement with an approximately circular cross-section ofthe pre-evaporation chamber 12 and the combustion chamber 2, the ratioD/d of the diameter D of the combustion chamber 2 to the diameter d ofthe pre-evaporation chamber 12 lies in the range: 1.2<D/d<3.0,preferably 1.4<D/d<2.6. The transition from the pre-evaporation chamber12 to the combustion chamber 2 takes the form of a neck portion, atwhich the cross-section widens abruptly in the main direction of flow H.Over the axial length of this neck portion, the flow conditionsestablished may additionally be purposefully adjusted, wherein the axiallength of the neck portion may also be selected in particular to be veryshort or the neck portion may also have substantially absolutely noaxial extent.

During operation, the combustion air is supplied with strong swirl tothe pre-evaporation chamber 12, which comprises the film evaporatorsurface 4 arranged to the rear of the combustion air inlets 8. In thisway, good intermixing of the supplied combustion air with evaporatingfuel takes place in the pre-evaporation chamber 12, to yield a fuel-airmixture which flows in the pre-evaporation chamber 12 with a hightangential flow component. Because of the significant widening of theflow cross-section at the point of transition from pre-evaporationchamber 12 to combustion chamber 2, significant radial widening of theswirl formed takes place, which is accompanied by a significant speedreduction in the axial direction, such that a recirculation region formsin the central region of the combustion chamber 2 close to the axis, inwhich recirculation region the gases flow contrary to the main directionof flow H. Furthermore, an axially symmetrical outer recirculation zonealso forms in the radially outer region of the combustion chamber 2directly downstream of the transition point. To achieve the describedflow conditions, the combustion air is preferably introduced with swirlof such a strength that a swirl number S in the range of 0.4<S<1.4,preferably 0.5<S<1.1, is established at the transition from thepre-evaporation chamber 12 to the combustion chamber 2. In this way,very good flow stabilization is achieved, which during operation resultsin particular in reliable anchoring of the flame in the combustionchamber 2.

As a result of the described refinement of the combustion chamberarrangement in the fourth embodiment, pre-processing of the evaporatedfuel with combustion air to yield an at least largely pre-mixed fuel-airmixture is achieved in a structurally very simple way, requiring only alittle structural space in the axial direction, so resulting in goodflow stabilization in the combustion chamber arrangement. In thismanner, particularly low-pollutant combustion is achieved in thecombustion chamber 2.

Modifications

The first modification of the fourth embodiment shown in FIG. 6 differsfrom the fourth embodiment shown in FIG. 5 in that the liquid fuel isnot supplied from radially outside to the film evaporator surface 4 butrather in the center of the rear wall 3 in the axial direction. As aresult of the arrangement of the film evaporator surface 4 axially tothe rear of the combustion air inlet 8 and the strong swirl of thesupplied combustion air, it is also possible in this case to achievereliable fuel evaporation and intermixing to yield a fuel-air mixture.

The refinement according to the first modification furthermore differsfrom the above-described fourth embodiment in that the ignition element11 does not project in the axial direction into the pre-evaporationchamber 12 but rather obliquely from the back and from radially outsideinto the pre-evaporation chamber 12.

Since the further features match the previously described fourthembodiment and the first modification also achieves the same advantagesas described above, a new description will be omitted.

The second modification of the fourth embodiment shown in FIG. 7 differsfrom the fourth embodiment shown in FIG. 5 only in that the fuel feed 9opens in the axial direction at the rear wall 3 of the pre-evaporationchamber 12 providing the film evaporator surface 4. In the secondmodification, the fuel feed 9 opens somewhat to the side of thelongitudinal axis Z in the radial direction.

The third modification of the fourth embodiment shown in FIG. 8 differsfrom the second modification merely in the configuration of thetransition from pre-evaporation chamber 12 to combustion chamber 2.

As FIG. 8 shows, although the flow cross-section at the transition frompre-evaporation chamber 12 to combustion chamber 2 in this case stillwidens very significantly, it does not do so quite so abruptly as itdoes in the fourth embodiment and the previously described modificationsthereof. In the third modification specifically depicted, anapproximately conical widening with a large opening angle is provided.Preferably, at least a double obtuse opening angle >90° is hereprovided.

In the fourth embodiment and the modifications thereof the individualstructural features may also be combined with one another in differentways. It is for example possible to provide the structural configurationof the transition from pre-evaporation chamber 12 to combustion chamber2 shown in the third modification also in the fourth embodiment or thefirst modification of the fourth embodiment.

1. A film evaporator burner arrangement comprising: a combustion chamberarrangement including a combustion chamber for reacting a fuel-airmixture with release of heat and which extends in an axial directionalong a longitudinal axis; a combustion air feed supplying combustionair with a tangential flow component to the combustion chamberarrangement at at least one combustion air inlet; a film evaporatorsurface evaporating liquid fuel starting from a fuel film arranged on arear wall axially to a rear of the combustion air inlet; and a fuel feedsupplying liquid fuel to the film evaporator surface.
 2. The filmevaporator burner arrangement as claimed in claim 1, in which thecombustion air is supplied from radially outside at the combustion airinlet.
 3. The film evaporator burner arrangement as claimed in claim 1,wherein the film evaporator surface is free of porous, absorbent bodies.4. The film evaporator burner arrangement as claimed in claim 1, whereinthe film evaporator surface extends predominantly perpendicular to thelongitudinal axis.
 5. The film evaporator burner arrangement as claimedin claim 1, wherein the combustion air feed supplies the combustion airwith the tangential flow component to the combustion chamber.
 6. Thefilm evaporator burner arrangement as claimed in claim 1, wherein thecombustion chamber arrangement includes a pre-evaporation chamberarranged flow wise upstream of the combustion chamber for conditioning afuel-air mixture prior to entry thereof into the combustion chamber. 7.The film evaporator burner arrangement as claimed in claim 6, whereinthe pre-evaporation chamber is separated from the combustion chamber bya partition wall extending radially inwards from a side wall of thecombustion chamber arrangement.
 8. The film evaporator burnerarrangement as claimed in claim 7, wherein the partition wall extendsradially inwards and axially rearwards from the side wall.
 9. The filmevaporator burner arrangement as claimed in claim 6, wherein thepre-evaporation chamber has a smaller flow cross-section than thecombustion chamber in a direction perpendicular to the longitudinal axisand the flow cross-section of the pre-evaporation chamber widensabruptly at a transition from the pre-evaporation chamber to thecombustion chamber.
 10. The film evaporator burner arrangement asclaimed in claim 6, wherein the combustion air feed supplies thecombustion air with the tangential flow component to the pre-evaporationchamber.
 11. The film evaporator burner arrangement as claimed in claim1, wherein the fuel feed supplies the fuel with a tangential directioncomponent radially from outside to the film evaporator surface.
 12. Thefilm evaporator burner arrangement as claimed in claim 1, wherein thecombustion chamber is free of constrictions or contractions over itsaxial extent.
 13. A mobile heating appliance with a film evaporatorburner arrangement as claimed in claim 1.